Lecture 13: DNA transcription Flashcards
(27 cards)
What are the 3 types of RNA that transcription can generate?
mRNAs (proteins), tRNAs, and rRNAs.
What is the role of rRNAs?
They serve as the backbone of the ribosome. The other ribosomal proteins bind to the rRNAs.
RNA synthesis proceeds from […] to […]
5’ to 3’
RNA synthesis is highly processive - explain what is meant by this.
The RNA polymerase can read very long genes while still staying associated to the template strand.
As the RNA polymerase moves along the DNA, it forms a […]
Transcription bubble
Transcription starts at […] and stops at [….]
Promoters, transcriptional terminators
Describe the structure of RNA.
It is mostly single stranded, but it also coils back on itself because it complementarily base pairs with itself.
How does the length of the mRNA compare to the length of the template?
It is shorter, because it doesn’t include the promoter strand on the DNA or the terminator. It spans from the +1 to the end of the antitrailer.
Where does translation take place relative to the structure of the DNA?
It takes place from the AUG (start of the coding region) or to the stop codon (UGA, UAG, or UAA).
What is the Shine-Dalgarno sequence and where is it located?
It is lcoated on the mRNA right before the start codon for translation. Its purpose is to recruit the ribosome to the mRNA upstream of the start codon to begin translation.
During RNA transcription, what is located at the start of the mRNA? Explain why.
There are 3 phosphates. This is because the first nucleotide in the chain is not linked to anything, so energy is not required and they’re not used. For the other nucleotides, energy is required to form a phosphodiester bond that links them, which requires 2 out of 3 phosphates. The rest are linked by only 1 phosphate.
The polymerase recognition site and RNA polymerase binding site are found on which strand of the bacterial DNA?
The non-template strand.
The -35 region, also called the […], has a consensus sequence of […]
RNA polymerase recognition site, TTGACA
The -10 region, also called the […], has a consensus sequence of […]
RNA polymerase binding site/pribnow box, TATAAT
Explain the concept behind consensus seuqneces.
The -10 and -35 regions have consensus sequences, which are the average typical sequence, but RNA polymerases can recognize variations on these sequences and still perform their function.
What are the two types of terminators for transcription in bacteria? What do they have in common?
Rho independent and Rho dependent. They are both organized such that the RNA being synthesized (usually) makes a hairpin with unpaired bases at the top, which stalls the RNA polymerase. This allows the RNA to detach from the DNA.
Explain what differentiates Rho independent transcriptional terminators from Rho dependent transcriptional terminators.
Rho independent has 6 uridines after the hairpin structure and make no use of the Rho factor, while Rho dependent has no poly(U) tract, needs the rho factor, and doesn’t always use the hairpin.
Describe how transcription termination works in Rho independent termination.
The RNA polymerase moves along DNA, synthesizing RNA, which folds as it goes along. Once it folds into this hairpin structure, the polymerase gets stalled there. This, plus the series of 6 U’s which have a weak base pairing with adenine, allows the polymerase and RNA to detach.
Describe how transcription termination works in Rho dependent termination.
The RNA polymerase moves along the DNA, synthesizing RNA, which folds as it goes along. Once it folds into this hairpin structure, the polymerase gets stalled there. There’s also the Rho factor, which has followed closely behind the polymerase and can now catch up. Since it is a helicase, it catches up and opens up the DNA-RNA link, allowing for the detatchment of the polymerase and the RNA.
Describe the difference between eucaryotic mRNA and procaryotic mRNA in terms of number of genes synthesized.
Eucaryotic: monocristronic - 1 mRNA = 1 protein
Procaryotic: multicistronic - genes organized in operons, so multiple genes can be transcribed at the same time with one promoter.
Describe the difference between eucaryotic mRNA and procaryotic mRNA in terms of cap structure.
Eucaryotic: cap structure added to 5’ end
Procaryotic: no cap structure
Describe the difference between eucaryotic mRNA and procaryotic mRNA in terms of tail.
Eucaryotic: Poly(A) tail added at the 3’ end
Procaryotic: No tail at the 3’ end
Describe the difference between eucaryotic mRNA and procaryotic mRNA interms of introns.
Eucaryotic: usually contains many introns
Procaryotic: in general, no introns (although some exceptions)
Describe the difference between eucaryotic mRNA and procaryotic mRNA in terms of transcription and translation location.
Eucaryotic: transcription occurs in the nucleus, while translation occurs in the cytoplasm.
Procaryotic: both processes occur in the cytoplasm and can thus be coupled, allowed for more efficiency.
